Heisenberg turns to the other two and says: “Clearly this is a joke, but how can we figure out if it’s funny or not?”

Place the joke inside a sealed box together with an mp3 player. The mp3 player is set to switch on and deliver the punch line when an atom of a radioactive element decays.

As long as the box remains sealed, then the joke is both funny and unfunny!

And in the same vein…

A cat with diabetes is placed inside a sealed box together with a device that will deliver it a chocolate biscuit when an atom of a radioactive element decays.

As long as the box remains sealed the cat can be considered to be simultaneously both normogycemic and hyperglycemic. Open the box and the wave function collapses (as does the cat if it has eaten the biscuit)

A duck walks into a bar and goes up to the bartender.
The bartender says "What can I get you?"
Duck: Umm. Do you have any grapes?
Bartender (looking surprised and finding the question odd):
No, I’m afraid we don’t.
And the duck waddles slowly out of the bar.

The next day at the same time, the duck waddles into the bar, hops up on a bar stool.
Bartender: Hi. What can I get for you?
Duck: Umm. Do you have any grapes?
Bartender (a little annoyed): Hey! Weren’t you in here yesterday. Look buddy, we don’t have any grapes. OK?

The duck hops off the stool and waddles out the door.

The next day, at the same time, the bartender is cleaning some glasses when he hears a familiar voice
Duck: Umm… Do you have any grapes?
The bartender is really ticked off.
Bartender: Look. What’s your problem? You came in here yesterday asking for grapes, I TOLD you, WE DON’T HAVE ANY GRAPES!! Next time I see your little ducktail waddle in here I’m going to nail those little webbed feet of yours to the floor. GOT me pal?

And the duck hops off the bar stool and waddles out.

The NEXT day at the same time, the duck waddles into the bar, walks up to the bartender and the bartender says,
"What the heck do YOU want?"
Umm. do you have any nails?
What!? OF course not.
Oh. Well, do you have any grapes?

One hot and dry day in the Wild West, this dog walks into a saloon and says, “Gimme a beer”. Evidently this type of thing wasn’t too rare 'round those parts because the bartender said, “I’m sorry, but we don’t serve dogs here.” The dog then took out a silver dollar, dropped it on the bar, and said, “Look, I got money, and I want a beer.” This scene had the potential to get ugly. The bartender, getting a little irate, said one more time, “We do not serve dogs here. Please leave.” The dog growled, so the bartender pulled out a gun and shot the dog in the foot! The dog yelped, and ran out the door.

The next day, the swinging bar doors were tossed open and in walks the dog that had been in the saloon the day before. He was dressed all in black. A black cowboy hat, a black vest, three black cowboy boots and one black bandage. The dog looks around, waits for the talking to quiet down, and says, “I’m lookin’ fer the man who shot my paw.”